The Misuse of Drugs Act is a drug control law in Singapore classifying substances into three categories, Classes A, B, and C. Section 44 provides that "The Minister may, by an order published in the Gazette" add, remove, or transfer drugs among the classes. The statute's penal provisions are draconian by most nations' standards, providing for long terms of imprisonment, caning, and capital punishment. The law creates a presumption of trafficking for certain threshold amounts, e.g. 30 grams of cannabis. It also creates a presumption that a person possesses drugs if he possesses the keys to a premises containing the drugs, and that "Any person found in or escaping from any place or premises which is proved or presumed to be used for the purpose of smoking or administering a controlled drug shall, until the contrary is proved, be presumed to have been smoking or administering a controlled drug in that place or premises." Thus, one runs the risk of arrest for drug use by simply being in the company of drug users. The law also allows officers to search premises and individuals, without a search warrant, if he "reasonably suspects that there is to be found a controlled drug or article liable to seizure". Moreover, Section 31 allows officers to demand urinalysis of suspected drug offenders.

Section 17 of the Misuse of Drugs Act[1] lists the amount of controlled drugs beyond which, the person who carries them shall be presumed to possess them for the purpose of drug trafficking unless proven otherwise:

The possession, consumption, manufacturing, import, export, or trafficking of these and other controlled drugs in any amount are illegal. Persons caught with less than the Mandatory Death Penalty amounts of these controlled substances face penalties ranging from caning[9] (up to 24 strokes) to life in prison. Pursuant to a law change in 2009, cannabis (marijuana) and marijuana mixtures (diluted with other substances) are treated the same under Singapore law—the presumed intent is trafficking.

cannabinol derivatives means the following substances, namely tetrahydro derivatives of cannabinol and their carboxylic acid derivatives, and 3-alkyl homologues of cannabinol or its tetrahydro derivatives;

coca leaf means the leaf of any plant of the genus Erythroxylon from whose leaves cocaine can be extracted either directly or by chemical transformation;

concentrate of opium poppy-straw means the material produced when poppy-straw has entered into a process for the concentration of its alkaloids;